on which floor is the floor assembly above the floor area / the storey

[sunyaer]

This is from Ontario building code 2012:
3.4.4.1. (1) is the counterpart of 9.9.4.2 in part 9.
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9.9.4.2. Fire Separation for Exits
(1) Except as provided in Sentence (5) and Article 9.9.8.5., every exit other than an exit doorway shall be separated
from each adjacent floor area or from another exit by a fire separation having a fire-resistance rating not less than that
required for the floor assembly above the floor area.

(2) Where there is no floor assembly above, the fire-resistance rating required in Sentence (1) shall not be less than that
required by Subsection 9.10.8. for the floor assembly below, but in no case shall the fire-resistance rating be less than
45 min.
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3.4.4.1. Fire-Resistance Rating of Exit Separations
(1) Except as provided by Sentences (2), (3) and (5) and Sentences 3.3.5.4.(3), 3.4.4.2.(2), 3.4.4.3.(1) and 3.13.3.1.(3),
every exit shall be separated from the remainder of the building by a fire separation having a fire-resistance rating not
less than that required by Subsection 3.2.2., but not less than 45 min, for,
(a) the floor assembly above the storey, or
(b) the floor assembly below the storey, if there is no floor assembly above

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Floor assembly is not a defined term. In a 3 storey (no basement) residential building, there is an exit shaft,

1). On the top storey of the shaft, which floor assembly should be used to determine the fire resistance rating for the shaft separation? The roof or the 3rd floor assembly?

2). On 2nd floor, which floor assembly should be used to determine the fire resistance rating for the shaft separation?

 

[tmurray]

Shafts are a "service space" and handled differently in Part 3. See 3.6.3.

In Part 9, you would just follow 9.10.8.1 for requirements. If the shaft has a floor above, it would need the associated floor rating. If it terminates at the roof, it would need the appropriate roof rating.